(1) Field of the Invention
The present invention generally relates to cooling garments for preventing heat-related illnesses. In particular, the present invention is directed to a cooling garment that includes phase change materials (PCM) positioned at the extremities of the wearer.
(2) Description of the Related Art
Generally speaking, the human body can tolerate cold environments rather well, but is very sensitive to hot environments. The body has a self-cooling mechanism in the form of evaporation of sweat. However, the body's self-cooling mechanism is limited in at least a couple of ways. First, it will only effectively cool the body at or below a certain ambient temperature and at humidity well under 100%. Second, body fluids must be replenished to sustain the self-cooling mechanism.
Heat strain and the more serious condition heat stress refer to the situation when humans are overheated to the degree that the core temperature is increased. Heat stress may result in various harmful physiological effects on the body's functions. If heat stress is combined with hard and stressful work, it may develop into a life-threatening condition known as heat stroke.
To minimize incidents of heat strain, heat stress, and heat stroke, most work areas are air-conditioned and/or individuals are provided with a locally-cooled environment in the form of a cooling garment, e.g., suit or vest, having cool water circulation or equivalent. Active cooling between work periods and air flow through a worker's uniform are additional ways to minimize incidents of heat-related injuries.
Cooling garments such as cooling vests and cooling suits generally include ice or a phase change material as a medium to reduce the user's elevated temperature and, in so doing, transform the cooling material from solid state to liquid state. In order to cope with a heat production of 300 Watts for a duration of one hour, a cooling suit typically has a weight of approximately 3 kilograms. The use of cooling garments may be problematic due to the high extra weight for some applications, difficulties with arranging a good heat transport from the body to the garment, and the time and effort needed to reactivate the garment after use, e.g., half an hour in ice-cold water. In addition, if ice is used for cooling, the vasoconstriction effect by restricting the blood flow counteracts the cooling capacity of ice.
Other approaches toward reducing core temperature relate to increased ambient airflow though the suit to enhance the body's cooling mechanism through sweating. By removing the humid air in the suit, more evaporation of sweat can take place and consequently give the body more cooling. The problem is that to be effective, high airflow of 200-300 liters/minute is needed, and the ambient air temperature must be some gradient below skin temperature. To take that from a portable air cylinder worn by the user (as with a self contained breathing apparatus (SCBA) commonly employed by fire fighters and other first responders) would reduce the duration of the SCBA too much. Wearable air cylinders would not have adequate capacity to support both the cooling and breathing requirements. The alternative of supplied air through a hose would reduce the user's movements and operating range.
Because existing cooling garments often work to insulate a wearer's body, thereby hindering the body's self-cooling mechanisms, existing cooling garments are often not effective for activities that require a high workload or for users that must be covered for protection against heat or harmful substances, e.g., fire fighters and responders to hazardous materials (HazMat) incidents. In these cases, users wearing existing cooling garments may still be subject to overheating and heat-related injuries.
Some products offer cooling of hands and arms after exposure to high heat, thereby reducing the core temperature. However, physiological data indicates that if a person has been exposed to heat stress, there is no way for him to recover in a short time. After the body has been overheated, a rest of days is suggested. Consequently, although some products are effective at quickly reducing the core temperature, they do not reduce the risk of heat stroke if more strenuous work is done the same day or without an appropriate period of rest.